''Rhodocactus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

in the

cactus A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the plant family Cactaceae (), a family of the order Caryophyllales comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, ...

family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

and a fully

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

-like habit. The genus was sunk into a broadly

circumscribed In geometry, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

'' Pereskia'', but

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies from 2005 onwards showed that with this circumscription ''Pereskia'' was

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

, and in 2016, ''Rhodocactus'' was restored for southern South American species.

Description

Like all cacti, ''Rhodocactus'' species have a

succulent In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...

habit and specialized structures,

areole In botany, areoles are small light- to dark-colored bumps on cactus, cacti out of which grow clusters of Thorns, spines, and prickles, spines. Areoles are important diagnostic features of cactus, cacti, and identify them as a family distinct fr ...

s, that bear spines. They differ from most cacti in having persistent leaves. They grow as trees, tall. When mature, their stems develop bark, but its development is delayed, and all the species other than '' Rhodocactus nemorosus'' retain

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

ta. The areoles of ''Rhodocactus'' species can form "brachyblasts", called "spur shoots" by Beat Leuenberger. The areole initially forms in the axil of a leaf (stage A in the diagram below). This leaf may be lost, leaving a leaf scar, and leaves may grow on the areole (stage B). The areole may then grow out to form a brachyblast – a short, very crowded shoot that bears leaves (stage C). Later this may form a longer, but still short shoot that has its own areoles (stage D). Asai and Miyata regard the formation of brachyblast leaves as a distinguishing characteristic of the genus in comparison to ''Pereskia''. ''Rhodocactus'' flowers are about in diameter. File:Areole and brachyblast development in Rhodocactus.svg, Areole and brachyblast development in ''Rhodocactus'' File:Pereskia grandifolia var. violacea 2020-02-08 7117.jpg, Areole on a young stem of ''R. grandiflorus'' is in the axis of the auxoblast leaf (stage A) File:Pereskia grandifolia 15zz crop.jpg, Areoles on this stem of ''R. grandiflorus'' have brachyblast leaves (stage B) File:Pereskia tampicana 1.jpg, Short shoot of ''R. grandiflorus'' (stage D)

Taxonomy

''Rhodocactus'' was originally described as a subgenus of '' Pereskia'' by

Alwin Berger Alwin Berger (28 August 1871 – 20 April 1931) was a German botanist best known for his contribution to the nomenclature of succulent plants, particularly agaves and cacti. Born in Germany he worked at the botanical gardens in Dresden and Fra ...

, and was raised to a genus in 1936 by Frederik Marcus Knuth. The genus was later sunk back into in a broadly defined genus ''Pereskia''.

Molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies from 2005 onwards suggested that when

in this way, ''Pereskia'' was not

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, and consisted of three clades. By 2016, each clade was recognized as a separate genus, one of which is ''Rhodocactus''. Only the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of Knuth's circumscription of the genus, '' Rhodocactus grandifolius'', belongs to the clade re-described as ''Rhodocactus''. The other species were mostly newly transferred from ''Pereskia''. A consensus

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

from a 2005 study is shown below with the more recent generic assignments added. It shows that the three genera are basal to the rest of the cacti.

Species

Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

accepted the following species: Species that have also been placed in ''Rhodocactus'' include: *''Rhodocactus bleo'' (F.M.Knuth) F.M.Knuth = '' Leuenbergeria bleo'' F.M.Knuth) Lodé *''Rhodocactus guamacho'' (F.A.C.Weber) F.M.Knuth = '' Leuenbergeria guamacho'' (F.A.C.Weber) Lodé *''Rhodocactus horridus'' (DC.) F.M.Knuth = '' Pereskia horrida'' D.C. *''Rhodocactus lychnidiflorus'' (D.C.) F.M.Knuth = '' Leuenbergeria lychnidiflora'' (D.C.) Lodé *''Rhodocactus portulacifolius'' (L.) F.M.Knuth = '' Leuenbergeria portulacifolia'' (L.) Lodé *''Rhodocactus zinniiflorus'' (D.C.) F.M.Knuth = '' Leuenbergeria zinniiflora'' (D.C.) Lodé

References

{{Taxonbar, from=Q15710774 Pereskioideae Cactaceae genera